Across the void Hubble sees the birth of stars

Stellar hurrucane: 42 million billion miles away and 7,000 years ago, the answers to cosmic mysteries are blowing in the wind

Saturday 4 November 1995 00:02 BST

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In the constellation of Serpens, more than 42 million billion miles away, an interstellar hurricane is tearing apart a vast cloud known as the Eagle nebula. As the dust and gas disperse, they have revealed to the watchful eye of the Hubble space telescope the birth-pangs of newborn stars.

The telescope's Wide Field and Planetary Camera has caught a striking image of vast columns of cool gas and dust reaching out from a cloud of hydrogen, like stalagmites from the floor of a cave. The gas inside the columns is dense enough to collapse under its own weight, forming young stars which continue to grow as they accumulate more material from their surroundings.

Released this week, the photographs capture events that took place 7,000 years ago, more than 1,000 years before the first Pharaoh ascended the throne of Egypt. Although light is the fastest thing in the universe, it has taken 7,000 years to cross the void between the nebula and the earth.

But astronomers are excited by more than just the beauty of the image, for it reveals hitherto unknown factors in the process of star formation which they had thought they understood. The stars from the Eagle nebula may be stunted from malnutrition.

The "wind" blowing across the Eagle nebula is actually a torrent of ultraviolet light from nearby young hot stars, heating the gas along the surface of the columns and boiling it off into space. The ghostly streamers flowing away from the columns in the picture are flows of this "photoevaporating" gas.

Not all the gas evaporates at the same rate, and as the outer layers disperse they reveal the denser globules within which the new stars are forming.

Jeff Hester of Arizona State University, whose team took the images, said "It's a bit like a wind storm in the desert. As the wind blows away the lighter sand, heavier rocks are uncovered. But instead of rocks, the ultraviolet light is uncovering the egg-like globules of gas that surround stars that were forming inside the gigantic gas columns."

Some of these "eggs" appear just as tiny bumps on the surface of the column or, if they have been uncovered, more fully as fingers of gas protruding from the larger cloud.

"This is the first time we have actually seen the process of forming stars being uncovered by photoevaporation," Dr Hester said. "In some ways, it seems more like archaeology than astronomy. The ultraviolet light from the nearby stars does the digging for us, and we study what is unearthed."

Eventually, the process of photoevaporation, by boiling off the gas, deprives the growing stars of the material from which they "feed". "We believe that the stars were continuing to grow as more and more gas fell on to them," Dr Hester said, but the process was cut short as the cloud of gas was dispersed.

Some astronomers believe that, left to its own devices, a star will continue to grow until it nears the point where nuclear fusion begins in its interior. When this happens, the star itself begins to blow a strong wind that clears away the residual material. The Eagle nebula is the first instance where they have seen an external wind blowing.

Sadly, however, the Hubble astronomers believe that photoevaporation may not only stunt the growth of the newborn stars, it may inhibit the formation of planets round such stars. It is not yet clear if these stars in the Eagle nebula have formed the discs that go on to become solar systems. According to Dr Hester, "if these discs haven't formed yet, they never will."

For astronomers, the Hubble space telescope's images of the Eagle nebula simply bear out that Bob Dylan was right: for the basic questions of star birth and the formation of planets "the answer, my friends, is blowing in the wind".